Magnetic resonance imaging (MRI) is used to diagnose a variety of cancers, including brain tumors. MRI, nuclear magnetic resonance (NMR), and other magnetic resonance (MR) apparatus, systems, and approaches continue to become more sophisticated, powerful, precise, and complicated. However, MRI continues to experience limits in image resolution due to hard physical and physiological limits. These physical realities have limited conventional systems to imaging tumors that are larger than 10 mm in diameter. Conventionally, T1-weighted images have been used by clinicians to assess brain abnormalities. However, these conventional assessments have been of limited value because conventional T1-weighted images and T2-weighted images are non-quantitative and their interpretation is necessarily subjective. Additionally, conventional T1 weighted and T2 weighted images have had inadequate resolution to detect very small tumors (e.g., less than 2 mm in diameter). T1 refers to spin-lattice relaxation and T2 refers to spin-spin relaxation.
MR involves the transmission of carefully controlled radio frequency (RF) energy in the presence of carefully controlled magnetic fields to produce NMR in a material exposed to the RF energy. Increasing the strength of the magnetic fields used in MRI to, for example, 7 T improves spatial resolution but reduces contrast. Thus, contrast agents have been employed to attempt to increase contrast. As the magnetic field is strengthened, higher frequencies are needed for the radio frequency (RF) to produce NMR because of the Larmor relationship:ω=γB0 
where:                ω is the precession frequency        γ is the gyromagnetic ratio, and        B0 is the magnetic field strength.        
Unfortunately, the higher frequencies used with the higher magnetic field strength also reduce the effectiveness of the conventional contrast agents used in MRI. For example, a contrast agent that produces a first change in T1 in a lower strength field may produce a second, lower change in T1 in a higher strength field.
Due to the physical and physiological limits, conventional 1.5 T or 3 T human scanners have typically been limited to a resolution of approximately 2×2×2 mm3. However, some targets to be evaluated using MRI (e.g., tumors, groups of cancer cells, individual cancer cells, proteins) may be significantly smaller than 2×2×2 mm3. For example, some tumor cells may be as small as 10 microns.
While various imaging modalities are used in clinical and surgical settings, MRI is a preferred method of brain tumor imaging prior to surgery. Conventionally, even though an NMR signal may have been acquired from a tumor or cancer cell that was less than the voxel size used in MR acquisition and reconstruction, it has been difficult, if even possible at all, to distinguish those voxels from voxels that do not include small targets. Targeted molecular contrast agents have facilitated improving the MRI assessment of tumors. However, the usefulness of conventional molecular contrast agents has been limited due to the masking effect of non-specific uptake or due to the limited time during which changes in contrast due to the molecular contrast agent are present.